Sum of odd numbers.sol

pragma solidity ^0.4.19;
contract Problem {
  function rowSumOddNumbers(int n) public pure returns (int) {
    int end = (1 + n ) * n - 1;
    int start = end - 2 * (n - 1);
    int sum = (start + end) * n / 2;
    return sum;
  }
}